The present invention relates to an electromagnetic deflection yoke apparatus for cathode-ray tubes, specifically a deflection yoke apparatus suited to in-line beam type color television cathode-ray tubes which is adapted to improve color distortion of a picture including rasters individually formed by three electron beams on a faceplate of the cathode-ray tube, particularly a narrow raster formed by a center electron beam, through a pair of U-shaped cores provided to be movable in a direction intersecting at right angles to the direction of an array of electron guns.
Recently, a conversionless type deflection yoke capable of adjusting dynamic convergence without employing an independent dynamic convergence system has been developed as a deflection yoke for an in-line color television cathode-ray tube. This deflection yoke is intended to adjust dynamic convergence by varying the distribution of windings of horizontal and vertical deflection coils or shifting and/or inclining the deflection yoke in all directions of three-dimensional coordinates expressed by X, Y and Z axes, thereby consequently varying the relative position of deflection flux which acts on electron beams.
In such a deflection yoke, the horizontal deflection coil is adapted to generate a pin cushion type deflection field and the vertical deflection coil to generate a barrel type deflection field. Under the effect of the above-mentioned deflection field, of three primary color electron beams emitted from three electron guns, that is blue, green and red electron guns disposed in in-line arrangement in the horizontal direction, the intensity of deflection field for the green electron beam emitted from the electron gun located at the center is smaller in the vertical deflection direction than the intensity of deflection fields for blue and red electron beams emitted from the electron guns located at both sides of the green electron gun. As a result, as shown in FIG. 1, three color electron beams deviate from one another at corners of the picture appearing on the faceplate of the cathode-ray tube; particularly, raster G formed by green beam 12 at the top and the bottom of the picture largely deviates inside from raster R and B formed by blue beam 10 and red beam 14.
Therefore when the above-mentioned type deflection yoke is to be used, magnetic devices are provided near the beam emission outlet of the electron gun on the neck of the cathode-ray tube, separately from the deflection yoke and a part of the deflection field generated from the horizontal and vertical deflection coils is separately introduced into the magnetic devices and this partial field is forced to mainly affect green beam 12 which is located at the center to supplementarily deflect in advance this green beam, thus improving narrow raster and misconvergence due to the green beam.
However, in such a system, a preliminary deflection field which affects beam 12 at the center is fixedly determined by the intensity of deflection field of both deflection coils and/or the shape or position of the magnetic device and therefore a desired adjustment cannot be carried out. When the deflection yoke is shifted, for example, in the axial direction of the cathode-ray tube, the magnetic device does not move following up the deflection yoke and accordingly the relative position of magnetic flux which acts on green beam 12 varies along with shifting of the deflection yoke whereby an optimum preliminary deflection field cannot be obtained at all times. Moreover, since the magnetic device is provided near the electron guns, for example, a focus will be adversely affected.
Accordingly, an object of the present invention is provide a deflection yoke apparatus for the in-line color television cathode-ray tube which does not cause color deviation of the raster due to the beam at the center of the faceplate.
Another object of the present invention is to provide a convergenceless type deflection yoke apparatus for the in-line television cathode-ray tube which does not cause a coma at the top and bottom of the picture.
Another object of the present invention is to provide a convergenceless type deflection yoke apparatus capable of improving a narrow raster and obtaining a satisfactory convergence at all positions on the picture without any deflection distortion of the focus and others.
Another object of the present invention is to provide an electromagnetic deflection yoke apparatus capable of free adjustment of the convergence of a narrow raster regardless of the positional state of the deflection yoke apparatus mounted on the cathode-ray tube.